Honestly, this is a great game, one of the best you ca find for the DS. The soundtrack is great, the puzzles are hard, the cases are somewhat interesting, but if you have played any of the other games your expecting this. There isn't much here you haven't seen before. Sure, now you can move around, and there are all new characters, but ignoring that this is SSDD people. Then again, I was hoping for that. I LOVED the Phoenix Wright games and more of it is just great. Just make sure you don't come to this game expecting something new, because it really isn't there. But, if your a fan of the series you'll like it. That's all there is to it people.
Oh, but it still wasn't as good as Trials and Tribulations. That game had the best story out of any of them because Godot was so AWESOME.
Apollo Justice suffered as a successor to the Phoenix Wright story arc because in addition to being too heavily attached to Phoenix Wright, it took it's puzzles to an almost absurd level of difficulty and obscurity. Investigations breaks free of the previous games, both in story and gameplay, and it ended up being one of the best Ace Attorney games in the series.
Despite taking place entirely outside of the courtroom, there still are segments consisting of listening to and discrediting witness testimony. However, the investigation portion of the game has gone through a bit of an overhaul. Two new major mechanics are introduced as well; Logic and Deduction.
As you examine crime scenes and talk with people, you pick up logic fragments that you can then piece together through an interface on the bottom screen. It's a pretty satisfying addition, as the solutions almost always make sense, and don't require the extreme amounts of abstract thinking the last Phoenix Wright game and Apollo Justice required.
Deduction, on the other hand, isn't quite as great. This basically is an added button that appears during first-person examinations which allows you to come to conclusions on something you're looking at using evidence. In most cases it works pretty well, but there are one or two obscure solutions that nearly stumped me.
Testimony is still handled the same way as it was in the previous Ace Attorney games. The actual solutions involved are much more logical compared to the courtroom sequences in the other games, so I did find myself enjoying this part of the game much more than I had previously. My only issue with it is that it was actually almost too easy in places---the hints you're given when testimony returns to the start are way too helpful and take a lot of the challenge out of the game.
Lastly (and this is the most minor gripe ever), the touch screen controls kind of suck for movement during side scrolling sequences, but you can use the dpad instead.